Long-term management and treatment of acute intermittent porphyria with recurring attacks using pharmacological prophylaxis.

BACKGROUND: There is no definitive guidance on whether patients with acute intermittent porphyria (AIP) with recurrent attacks need pharmacological prophylactic treatment. METHODS: The management strategies for patients with frequent (defined as ≥4 annualized attack rate (AAR) and less frequent attacks (<4 AAR), including treatment for acute attacks and duration of prophylaxis (weekly heme arginate 3 mg/kg body weight and/or investigational drug, givosiran), were summarized. The AAR for the following periods were presented: the first 2 years after diagnosis, before/after prophylaxis, and the most recent 2 years. RESULTS: A total of 29 patients with AIP were included, 19 (34.5%) had <4 AAR and 10 (65.6%) had ≥4 AAR in the first 2 years after diagnosis. All patients experienced reduced attacks during the treatment course, 23 (79.3%) were attack-free during the most recent 2 years. Among the 9 patients who received prophylaxis (7 heme arginate; 1 givosiran, 1 heme arginate followed by givosiran), 5 (55.6%) were attack-free in the most recent 2-year period and prophylaxis was discontinued because there had been no attacks for >1 year. For patients without prophylaxis (n = 20), 18 (90.0%) were attack-free in the most recent 2-year period and 15 (75.0%) experienced attacks only in the first 2 years after diagnosis. CONCLUSIONS: Prophylaxis could be considered for patients with AIP with ≥4 biochemically confirmed attacks/year after routine treatment of 1-2 years, during which the severity and frequency of attacks should be closely monitored to determine the necessity of pharmacologic prophylaxis. More studies are needed to reach a consensus on the use of pharmacological prophylaxis and treatment of AIP.

Persistir y no desistir: diagnosticando un caso de porfiria aguda intermitente / Persist and do not give up: diagnosing a case of acute intermittent porphyria

A young woman with a history of asthma and anxiety-depressive syndrome, with poor adherence to treatment in long follow-up by Psychiatry and Family Medicine. She consulted for persistent abdominal pain refractory to conventional analgesia, associated with hypertension, hyponatremia, and progressive muscle weakness. It was performed a first Hoesch test which was positive; however, the study of porphyrins in blood and urine was inconclusive. On the other hand, she presented an acute respiratory failure requiring transfer to the ICU. A second Hoesch test was repeated, remaining positive, in addition to the presence of an increase in porphobilinogen in 24-hour urine and delta-aminolevulinic acid. Genetic study was performed, being compatible with acute intermittent porphyria. Treatment with carbohydrates and hemin was started with an adequate response. Approval of givosiran (RNA interference drug) has been requested. The patient has shown clinical improvement. Due to functional deterioration, she required rehabilitation support. (AU)

Mujer joven con antecedentes de asma y síndrome ansioso-depresivo con escasa adherencia al tratamiento, en seguimiento por Psiquiatría y Médico de Familia desde hace años. Consultó por dolor abdominal persistente y refractario a analgesia convencional, junto con hipertensión, hiponatremia y debilidad muscular progresiva. Se realizó un primer test de Hoesch que fue positivo, aunque el estudio inicial de porfirinas en sangre y orina no fue concluyente. Posteriormente presentó insuficiencia respiratoria aguda, precisando traslado a UCI. Se repitió el test de Hoesch, nuevamente positivo, además de hallar incremento de porfobilinógeno en orina de 24 horas y de ácido delta-aminolevulínico. El estudio genético fue compatible con porfiria aguda intermitente. Recibió tratamiento con carbohidratos y hemina con adecuada respuesta. Está pendiente de aprobación de givosiran (fármaco ARN de interferencia). Ha evolucionado favorablemente, precisando soporte rehabilitador por marcado deterioro funcional. (AU)

[Acute hepatic porphyrias]. / Akute hepatische Porphyrien.

Acute porphyrias are caused by rare hereditary disorders of hepatic heme biosynthesis. Episodes of accumulating neurotoxic metabolites lead to multisystemic symptoms such as visceral pain, autonomic dysregulation, neurocognitive impairment, hyponatremia, and occasionally motor paralysis. In addition to protracted non-emergency courses, acute life-threatening crises can occur, often triggered by infection, medication, fasting, or hormonal stimuli. Since the clinical presentation is nonspecific and multifaceted, many patients have gone through a long odyssey until they receive a diagnosis. Acute attacks often lead to presenting initially to the emergency department, where acute hepatic porphyria (AHP) is easily overlooked in the differential diagnosis. Establishing the diagnosis requires a high level of genuine suspicion (e.g., cluster of signs and symptoms along with certain patterns of health care resource utilization). The initial diagnostic work-up requires the measurement of metabolites in the urine. Emergency management consists of infusions of glucose and heme arginate along with symptomatic therapy. However, porphyrinogenic agents must be strictly avoided ( www.drugs-porphyria.org ). After initial diagnosis, a thorough work-up should be done at a porphyria center (confirming the diagnosis, education, genetic counselling) and issuance of an emergency identification card is mandatory. If the frequency of relapses is high, new targeted prophylactic therapies have proven effective. Patients with known porphyria require special attention in any acute medical condition in order to avoid porphyrinogenic triggers and to exclude threatening differential diagnosis (e.g., sepsis) by consistent basic diagnostics.

Cimetidine Does Not Inhibit 5-Aminolevulinic Acid Synthase or Heme Oxygenase Activity: Implications for Treatment of Acute Intermittent Porphyria and Erythropoietic Protoporphyria.

Acute intermittent porphyria (AIP) is characterized by acute neurovisceral attacks that are precipitated by the induction of hepatic 5-aminolevulinic acid synthase 1 (ALAS1). In erythropoietic protoporphyria (EPP), sun exposure leads to skin photosensitivity due to the overproduction of photoreactive porphyrins in bone marrow erythroid cells, where heme synthesis is primarily driven by the ALAS2 isozyme. Cimetidine has been suggested to be effective for the treatment of both AIP and EPP based on limited case reports. It has been proposed that cimetidine acts by inhibiting ALAS activity in liver and bone marrow for AIP and EPP, respectively, while it may also inhibit the hepatic activity of the heme catabolism enzyme, heme oxygenase (HO). Here, we show that cimetidine did not significantly modulate the activity or expression of endogenous ALAS or HO in wildtype mouse livers or bone marrow. Further, cimetidine did not effectively decrease hepatic ALAS activity or expression or plasma concentrations of the putative neurotoxic porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG), which were all markedly elevated during an induced acute attack in an AIP mouse model. These results show that cimetidine is not an efficacious treatment for acute attacks and suggest that its potential clinical benefit for EPP is not via ALAS inhibition.

Long-term Remission of Acute Intermittent Porphyria Treated with Gonadotropin-Releasing Hormone Analogues and Estrogen: a Case Report.

BACKGROUND: Acute intermittent porphyria (AIP) is an autosomal dominant hepatic porphyria characterized by a partial deficiency of hydroxymethylbilane synthase involved in heme biosynthesis. It is difficult for all patients to achieve complete control of AIP episodes. METHOD: We report on a 20-year-old female woman who suffered from recurrent abdominal pain and was diagnosed as "acute intermittent porphyria". She failed to respond to conventional symptomatic treatment and subsequently was treated with gonadotropin-releasing hormone analogues (GnRH) combined with estrogen for one year. RESULT: The case did not experience acute attacks and obtained long-term clinical remission to date. CONCLUSIONS: GnRH combined with estrogen, one of the treatment options for menstrual-associated AIP, might induce long-term remission.

EXPLORE B: A prospective, long-term natural history study of patients with acute hepatic porphyria with chronic symptoms.

One-year data from EXPLORE Part A showed high disease burden and impaired quality of life (QOL) in patients with acute hepatic porphyria (AHP) with recurrent attacks. We report baseline data of patients who enrolled in EXPLORE Part B for up to an additional 3 years of follow-up. EXPLORE B is a long-term, prospective study evaluating disease activity, pain intensity, and QOL in patients with AHP with ≥1 attack in the 12 months before enrollment or receiving hemin or gonadotropin-releasing hormone prophylaxis. Data were evaluated in patients with more (≥3 attacks or on prophylaxis treatment) or fewer (<3 attacks and no prophylaxis treatment) attacks. Patients in the total population (N = 136), and more (n = 110) and fewer (n = 26) attack subgroups, reported a median (range) of 3 (0-52), 4 (0-52), and 1 (0-2) acute attacks, respectively, in the 12 months prior to the baseline visit. Pain, mood/sleep, digestive/bladder, and nervous system symptoms were each experienced by ≥80% of patients; most received hemin during attacks. Almost three-quarters of patients reported chronic symptoms between attacks, including 85% of patients with fewer attacks. Pain intensity was comparable among both attack subgroups; most patients required pain medication. All groups had diminished QOL on the EuroQol visual analog scale and the European Organisation for Research and Treatment of Cancer Quality-of-life Questionnaire Core 30 versus population norms. Patients with AHP with recurrent attacks, even those having fewer attacks, experience a high disease burden, as evidenced by chronic symptoms between attacks and impaired QOL.

Hemina para o tratamento de mulheres com ataques de porfiria aguda intermitente relacionados com o ciclo menstrual / Hemin for the treatment of women with attacks of acute intermittent porphyria related to the menstrual cycle

INTRODUÇÃO: A porfiria aguda intermitente (PAI) é um erro inato do metabolismo da biossíntese do heme, que acomete principalmente mulheres em idade menstrual. A doença se manifesta clinicamente com sintomas neuroviscerais agudos que podem ser esporádicos ou recorrentes, e que são potencialmente fatais. No Brasil, no âmbito do Sistema Único de Saúde (SUS), não há um Protocolo Clínico e Diretrizes Terapêuticas sobre o cuidado de Porfirias. Tendo em vista que a hemina (Panhematin®) é aprovada pela Anvisa para o tratamento dos ataques recorrentes de PAI relacionados com o ciclo menstrual em mulheres afetadas, quando o tratamento inicial com glicose é sabido ou suspeito de ser inadequado, o presente relatório foi desenvolvido com o objetivo de compreender a viabilidade da incorporação desse medicamento no SUS. PERGUNTA DE PESQUISA: O uso de hemina (Panhematin®) é eficaz, seguro e custo-efetivo para o tratamento de mulheres com ataques de PAI relacionados com o ciclo menstrual? EVIDÊNCIAS CLÍNICAS: Foi realizada uma revisão sistemática a partir de buscas nas bases de dados MEDLINE (via Pubmed); EMBASE; Cochrane Library; PEDRO; LILACS, IBECS BINACIS e BRISA/RedTESA (via BVS); OpenGrey; e ClinicalTrials.gov; considerando o tratamento de ataques agudos de PAI, em mulheres com idade igual ou maior a 16 anos, com hemina (Panhematin®). Foram estabelecidos critérios de elegibilidade abrangentes diante da escassez de evidências, mas ainda assim não foi encontrado nenhum ECR ou estudo observacional comparativo com resultados publicados. Foram incluídas três séries de casos que avaliaram pacientes com diferentes tipos de porfirias e sexos e 18 relatos de casos sobre mulheres com PAI. Em relação a eficácia, a redução da dor com o uso da hemina sugere que o medicamento contribua para a resolução de ataques porfíricos, mas a certeza dessa evidência é muito baixa. Somente 6 dos 18 relatos de casos avaliaram dor, sem que nenhum tenha avaliado o desfecho através de escalas, sejam elas validadas ou não. Esses estudos referiram melhora da dor na maioria dos casos. Quinze dos dezoito relatos de casos apresentam resultados para níveis urinários de ALA e PBG, sugerindo que a hemina contribui para a redução desses marcadores. Entretanto, deve-se levar em consideração a limitação das conclusões que podem ser tiradas a partir desse tipo de estudo. Quanto à segurança, os dados também são muito escassos. Duas séries de casos e três relatos de casos descreveram resultados para eventos adversos graves e não foram identificadas novas preocupações além daquelas descritas em bula. Todas as evidências incluídas neste relatório apresentaram risco de viés muito alto ou alto e certeza do conjunto de evidências avaliado como muito baixa, de acordo com o GRADE. Mais estudos são necessários para permitir conclusões mais robustas acerca da eficácia e, sobretudo, da segurança do medicamento. AVALIAÇÃO ECONÔMICA: Foi elaborado um modelo de custo-efetividade, baseando-se no desfecho de mortalidade, sob a perspectiva do SUS, com horizonte temporal de um ano, e incluindo apenas custos diretos (de tratamento com as terapias selecionadas e de internação). A análise foi conduzida a partir de em um modelo de árvore de decisão que projetou a relação entre custo da intervenção (hemina + glicose) e do comparador (glicose). O resultado da razão de custoefetividade incremental (RCEI) da hemina em comparação à glicose foi de R$ 1.101.525,27por vida salva, variando de R$450.511,78 a R$5.477.345,10 por vida salva na análise de sensibilidade probabilística. ANÁLISE DE IMPACTO ORÇAMENTÁRIO: Adotou-se uma perspectiva epidemiológica considerando os dados de prevalência e incidência de PAI disponíveis em literatura e aplicados ao contexto do Brasil, bem como proporção de mulheres que tinham a condição, o número de ataques e a utilização de hemina para o tratamento das crises. Foram considerados os mesmos recursos e custos associados utilizados na análise de custo-efetividade, assumindo disponibilidade da hemina no mercado de forma progressiva. A incorporação da hemina (Panhematin®), no SUS, geraria um impacto incremental de cerca de R$ 11,1 milhões no primeiro ano, atingindo quase R$ 83 milhões em cinco anos. MONITORAMENTO DO HORIZONTE TECNOLÓGICO: não foram detectadas tecnologias para compor o esquema terapêutico de ataques de PAI relacionados com o ciclo menstrual. Vale ressaltar que o medicamento givosirana foi identificado nas buscas, entretanto, o ensaio clínico identificado no Clinicaltrials avalia o uso da givosirana no tratamento de porfirias hepáticas agudas de forma geral, sem especificar a inclusão de PAI relacionada ao ciclo menstrual. O mesmo acontece para a indicação clínica do medicamento aprovada na Anvisa (2020), FDA (2019) e EMA (2020). CONSIDERAÇÕES FINAIS: há escassez de evidências sobre a eficácia e segurança da hemina (Panhematin®) e as evidências disponíveis provém apenas de séries de casos e relatos de casos, o que torna a avaliação de eficácia e segurança um desafio. Além do delineamento dos estudos, a descrição incompleta e a avaliação subjetiva dos resultados são outras dificuldades. As limitações acabam por se estender para as análises econômicas, as quais foram baseadas em estudos que não atendiam à indicação de bula da tecnologia. A análise de custo-efetividade incremental e o impacto orçamentário mostram valores expressivos e a incorporação dela indica não colaborar para a sustentabilidade do SUS, embora a hemina seja a única alternativa farmacológica comercializada atualmente para o manejo de crises de PAI. RECOMENDAÇÃO PRELIMINAR: os membros presentes no plenário da Conitec, em sua 110ª Reunião Ordinária, realizada no dia 06 de julho de 2022, deliberaram que a matéria fosse disponibilizada em consulta pública com recomendação preliminar desfavorável à incorporação de Panhematin® para o tratamento da porfiria aguda intermitente relacionados com o ciclo menstrual. Para essa recomendação, a Conitec considerou que as evidências acerca da eficácia e segurança do medicamento são escassas e de baixa qualidade. RECOMENDAÇÃO FINAL DA CONITEC: Pelo exposto, o Plenário da Conitec, em sua 112ª Reunião Ordinária, realizada no dia 31 de agosto de 2022, deliberou por unanimidade recomendar a não incorporação da hemina para o tratamento da porfiria aguda intermitente relacionados com o ciclo menstrual. Os membros da Conitec consideraram que não houve argumentação suficiente para a mudança de entendimento acerca da recomendação preliminar, principalmente considerando as evidências para eficácia e segurança da tecnologia, inclusive após contribuição presente de especialista no assunto. Foi assinado o Registro de Deliberação nº 768/2022. DECISÃO: não incorporar, no âmbito do Sistema Único de Saúde - SUS, a hemina para o tratamento da porfiria aguda intermitente relacionada com o ciclo menstrual, conforme a Portaria nº 110, publicada no Diário Oficial da União nº 184, seção 1, página 76, em 27 de setembro de 2022.

Acute intermittent porphyria: is oseltamivir safe in these patients?

A 40-year-old man attended the emergency room with abdominal pain and inappropriate behaviour associated with stress, and the consumption of alcohol and cannabis. Examination revealed hypertension (155/100 mmHg), tachycardia (95 beats per minute), abdominal pain and leucocytosis with neutrophilia, hyponatraemia and hypokalaemia. Urine was positive for nitrites, elevated bilirubin and cannabinoids. The patient was diagnosed with acute intermittent porphyria (AIP) and immediately treated. After initial treatment, the patient improved. However, he subsequently relapsed after initiating treatment with oseltamivir for a flu-like illness. Treatment was discontinued and the patient progressed favourably. AIP recurrence could have been mediated by oseltamivir; an association not previously described in the literature.

Mechanistic modelling of enzyme-restoration effects of new recombinant liver-targeted proteins in acute intermittent porphyria.

BACKGROUND AND PURPOSE: Acute intermittent porphyria (AIP) is a rare disease caused by a genetic mutation in the hepatic activity of the porphobilinogen-deaminase. We aimed to develop a mechanistic model of the enzymatic restoration effects of a novel therapy based on the administration of different formulations of recombinant human-PBGD (rhPBGD) linked to the ApoAI lipoprotein. This fusion protein circulates in blood, incorporating into HDL and penetrating hepatocytes. EXPERIMENTAL APPROACH: Single i.v. dose of different formulations of rhPBGD linked to ApoAI were administered to AIP mice in which a porphyric attack was triggered by i.p. phenobarbital. Data consist on 24 h urine excreted amounts of heme precursors, 5-aminolevulinic acid (ALA), PBG and total porphyrins that were analysed using non-linear mixed-effects analysis. KEY RESULTS: The mechanistic model successfully characterized over time the amounts excreted in urine of the three heme precursors for different formulations of rhPBGD and unravelled several mechanisms in the heme pathway, such as the regulation in ALA synthesis by heme. Treatment with rhPBGD formulations restored PBGD activity, increasing up to 51 times the value of the rate of tPOR formation estimated from baseline. Model-based simulations showed that several formulation prototypes provided efficient protective effects when administered up to 1 week prior to the occurrence of the AIP attack. CONCLUSION AND IMPLICATIONS: The model developed had excellent performance over a range of doses and formulation type. This mechanistic model warrants use beyond ApoAI-conjugates and represents a useful tool towards more efficient drug treatments of other enzymopenias as well as for acute intermittent porphyria.

Recombinant porphobilinogen deaminase targeted to the liver corrects enzymopenia in a mouse model of acute intermittent porphyria.

Correction of enzymatic deficits in hepatocytes by systemic administration of a recombinant protein is a desired therapeutic goal for hepatic enzymopenic disorders such as acute intermittent porphyria (AIP), an inherited porphobilinogen deaminase (PBGD) deficiency. Apolipoprotein A-I (ApoAI) is internalized into hepatocytes during the centripetal transport of cholesterol. Here, we generated a recombinant protein formed by linking ApoAI to the amino terminus of human PBGD (rhApoAI-PBGD) in an attempt to transfer PBGD into liver cells. In vivo experiments showed that, after intravenous injection, rhApoAI-PBGD circulates in blood incorporated into high-density lipoprotein (HDL), penetrates into hepatocytes, and crosses the blood-brain barrier, increasing PBGD activity in both the liver and brain. Consistently, the intravenous administration of rhApoAI-PBGD or the hyperfunctional rApoAI-PBGD-I129M/N340S (rApoAI-PBGDms) variant efficiently prevented and abrogated phenobarbital-induced acute attacks in a mouse model of AIP. One month after a single intravenous dose of rApoAI-PBGDms, the protein was still detectable in the liver, and hepatic PBGD activity remained increased above control values. A long-lasting therapeutic effect of rApoAI-PBGDms was observed after either intravenous or subcutaneous administration. These data describe a method to deliver PBGD to hepatocytes with resulting enhanced hepatic enzymatic activity and protection against AIP attacks in rodent models, suggesting that the approach might be an effective therapy for AIP.

Givosiran in acute intermittent porphyria: A personalized medicine approach.

BACKGROUND: In patients with acute intermittent porphyria (AIP), induction of delta aminolevulinic acid synthase 1 (ALAS1) leads to haem precursor accumulation that may cause recurring acute attacks. In a recent phase III trial, givosiran significantly reduced the attack rate in severe AIP patients. Frequent adverse events were injection-site reaction, fatigue, nausea, chronic kidney disease and increased alanine aminotransferase. OBJECTIVES: To describe the efficacy and safety of givosiran based on a personalized medical approach. METHODS: We conducted a retrospective patient file study in 25 severe AIP patients treated with givosiran in France. We collected data on clinical and biochemical efficacy along with reports of adverse events. RESULTS: Givosiran drastically reduced the attack rate in our cohort, as 96% were attack-free at the time of the study. The sustained efficacy of givosiran in most patients allowed us to personalize dosing frequency. In 42%, givosiran was only given when haem precursor levels were increasing. Our data suggest that givosiran is most effective when given early in the disease course. We confirmed a high prevalence of adverse events. One patient discontinued treatment due to acute pancreatitis. All patients had hyperhomocysteinemia, and all patients with initial homocysteine levels available showed an increase under treatment. In this context, one patient was diagnosed with pulmonary embolism. CONCLUSION: The sustained effect of givosiran allowed a decrease in dosing frequency without compromising treatment efficacy. The high prevalence of adverse events emphasizes the importance of restricting the treatment to severe AIP and administering the minimum effective dose for each patient.

Efficacy and safety of givosiran for acute hepatic porphyria: 24-month interim analysis of the randomized phase 3 ENVISION study.

BACKGROUND & AIMS: Upregulation of hepatic delta-aminolevulinic acid synthase 1 with accumulation of potentially toxic heme precursors delta-aminolevulinic acid and porphobilinogen is fundamental to the pathogenesis of acute hepatic porphyria. AIMS: evaluate long-term efficacy and safety of givosiran in acute hepatic porphyria. METHODS: Interim analysis of ongoing ENVISION study (NCT03338816), after all active patients completed their Month 24 visit. Patients with acute hepatic porphyria (≥12 years) with recurrent attacks received givosiran (2.5 mg/kg monthly) (n = 48) or placebo (n = 46) for 6 months (double-blind period); 93 received givosiran (2.5 mg or 1.25 mg/kg monthly) in the open-label extension (continuous givosiran, n = 47/48; placebo crossover, n = 46/46). Endpoints included annualized attack rate, urinary delta-aminolevulinic acid and porphobilinogen levels, hemin use, daily worst pain, quality of life, and adverse events. RESULTS: Patients receiving continuous givosiran had sustained annualized attack rate reduction (median 1.0 in double-blind period, 0.0 in open-label extension); in placebo crossover patients, median annualized attack rate decreased from 10.7 to 1.4. Median annualized days of hemin use were 0.0 (double-blind period) and 0.0 (open-label extension) for continuous givosiran patients and reduced from 14.98 to 0.71 for placebo crossover patients. Long-term givosiran led to sustained lowering of delta-aminolevulinic acid and porphobilinogen and improvements in daily worst pain and quality of life. Safety findings were consistent with the double-blind period. CONCLUSIONS: Long-term givosiran has an acceptable safety profile and significantly benefits acute hepatic porphyria patients with recurrent attacks by reducing attack frequency, hemin use, and severity of daily worst pain while improving quality of life.

Severe homocysteinemia in two givosiran-treated porphyria patients: is free heme deficiency the culprit?

Givosiran is a novel approach to treat patients with acute intermittent porphyrias (AIP) by silencing of ∂-ALA-synthase 1, the first enzyme of heme biosynthesis in the liver. We included two patients in the Envision study who responded clinically well to this treatment. However, in both patients, therapy had to be discontinued because of severe adverse effects: One patient (A) developed local injection reactions which continued to spread all over her body with increasing number of injections and eventually caused a severe systemic allergic reaction. Patient B was hospitalized because of a fulminant pancreatitis. Searching for possible causes, we also measured the patients plasma homocysteine (Hcy) levels in fluoride-containing collection tubes: by LC-MS/MS unexpectedly, plasma Hcy levels were 100 and 200 in patient A and between 100 and 400 µmol/l in patient B. Searching for germline mutations in 10 genes that are relevant for homocysteine metabolism only revealed hetero- and homozygous polymorphisms in the MTHFR gene. Alternatively, an acquired inhibition of cystathionine-beta-synthase which is important for homocysteine metabolism could explain the plasma homocysteine increase. This enzyme is heme-dependent: when we gave heme arginate to our patients, Hcy levels rapidly dropped. Hence, we conclude that inhibition of ∂-ALA-synthase 1 by givosiran causes a drop of free heme in the hepatocyte and therefore the excessive increase of plasma homocysteine. Hyperhomocysteinemia may contribute to the adverse effects seen in givosiran-treated patients which may be due to protein-N-homocysteinylation.

Dysregulation of homocysteine homeostasis in acute intermittent porphyria patients receiving heme arginate or givosiran.

Acute intermittent porphyria (AIP) is a rare metabolic disease caused by mutations within the hydroxymethylbilane synthase gene. Previous studies have reported increased levels of plasma total homocysteine (tHcy) in symptomatic AIP patients. In this study, we present long-term data for tHcy and related parameters for an AIP patient cohort (n = 37) in different clinical disease-states. In total, 25 patients (68%) presented with hyperhomocysteinemia (HHcy; tHcy > 15 µmol/L) during the observation period. HHcy was more frequent in AIP patients with recurrent disease receiving heme arginate, than in nonrecurrent (median tHcy: 21.6 µmol/L; range: 10-129 vs median tHcy: 14.5 µmol/L; range 6-77). Long-term serial analyses showed a high within-person tHcy variation, especially among the recurrent patients (coefficient of variation: 16.4%-78.8%). HHcy was frequently associated with low blood concentrations of pyridoxal-5'-phosphate and folate, while cobalamin concentration and the allele distribution of the methylene-tetrahydrofolate-reductase gene were normal. Strikingly, 6 out of the 9 recurrent patients who were later included in a regime of givosiran, a small-interfering RNA that effectively reduced recurrent attacks, showed further increased tHcy (median tHcy in 9 patients: 105 µmol/L; range 16-212). Screening of amino acids in plasma by liquid-chromatography showed co-increased levels of methionine (median 71 µmol/L; range 23-616; normal <40), suggestive of acquired deficiency of cystathionine-ß-synthase. The kynunerine/tryptophan ratio in plasma was, however, normal, indicating a regular metabolism of tryptophan by heme-dependent enzymes. In conclusion, even if HHcy was observed in AIP patients receiving heme arginate, givosiran induced an aggravation of the dysregulation, causing a co-increase of tHcy and methionine resembling classic homocystinuria.

Givosiran: A Review in Acute Hepatic Porphyria.

Givosiran (Givlaari®) is an δ-aminolevulinic acid synthase 1 (ALAS1)-directed small interfering RNA (siRNA) approved for the treatment of acute hepatic porphyria (AHP). In the phase 3 ENVISION trial, givosiran significantly reduced the annualized rate of composite porphyria attacks (i.e. attacks requiring hospitalization, urgent healthcare visit or intravenous hemin administration at home) compared with placebo in patients with recurrent acute intermittent porphyria (the most common type of AHP) attacks. Givosiran also improved several other outcomes, including hemin use and pain (the cardinal symptom of AHP). While generally well tolerated with an acceptable safety profile, the drug may increase the risk of hepatic and kidney adverse events. Givosiran offers the convenience of once-monthly subcutaneous administration. Available evidence indicates that givosiran is an important newer therapeutic option for patients with AHP and severe recurrent attacks.